Hsi-Jen Pan

Hydrogen-sensitive characteristics of a novel Pd/InP MOS Schottky diode hydrogen sensor

Steady-state and transient hydrogen-sensing characteristics of a novel Pd/InP metal-oxide-semiconductor (MOS) Schottky diode under atmospheric conditions are presented and studied. In presence of oxide layer, the significant increase of barrier height improves the hydrogen sensitivity even at lower operating temperatures. Even at a very low hydrogen concentration environment, e.g., 15 ppm H/sub 2/ in air, a significant response is obtained. Two effects, i.e., the removal of Fermi-level pinning caused by the donor level in the oxide and the reduction of Pd metal work function dominate the hydrogen sensing mechanism. Furthermore, the reaction kinetics incorporating the water formation upon hydrogen adsorption is investigated. The initial heat of adsorption for the Pd/oxide interface is estimated to be 0.42 eV/hydrogen atom. The coverage dependent heat of adsorption plays an important role in hydrogen response under steady-state conditions. In accordance with the Temkin isotherm behavior, the theoretical prediction of interface coverage agrees well with the experimental results over more than three decades of hydrogen partial pressure.

Comparative Hydrogen-Sensing Study of Pd/GaAs and Pd/InP Metal-Oxide-Semiconductor Schottky Diodes

In this work, the hydrogen response characteristics and sensing properties of catalytic Pd metal-oxide-semiconductor (MOS) Schottky diodes based on both GaAs and InP substrates are comparatively investigated. The behaviors of interface Fermi-level pinning causing the apparent difference in the barrier height modulation and the sensitivity are discussed. Furthermore, the effects of temperature and hydrogen concentration in the initial rate of change in current and the response time are examined. In order to study the steady-state reaction kinetics, we also performed the Langmuir analysis to estimate the values of initial heat of adsorption for both devices. Based on the adsorption isotherm of Temkin type, the interface coverage dependent heat of adsorption is responsible for the wide hydrogen sensing range. From the theoretical prediction, both devices have a very low sensitivity limit under atmospheric conditions.

High-performance InGaP/In x Ga/sub 1-x/As HEMT with an inverted delta-doped V-shaped channel structure

This letter reports a new and high-performance InGaP/In/sub x/Ga/sub 1-x/As high electron mobility transistor (HEMT) with an inverted delta-doped V-shaped channel. Due to the presence of V-shaped inverted delta-doped InGaP/In/sub x/Ga/sub 1-x/As structure, good carrier confinement and a flat and wide transconductance operation regime are expected. Experimentally, the fabricated device (1/spl times/100 /spl mu/m/sup 2/) shows a high gate-to-drain breakdown voltage of 30 V and a high output drain saturation current density of 826 mA/mm at V/sub GS/=2.5 V. The high transconductance expands over a very broad operation range with the maximum value of 201 mS/mm at 300 K. Meanwhile, the studied device exhibits a good microwave frequency linearity.

Temperature-dependent study of a lattice-matched InP/InGaAlAs heterojunction bipolar transistor

In this work, we report the temperature-dependent characteristics of a new InP/InGaAlAs heterojunction bipolar transistor (HBT). In order to improve the dc performance of conventional InGaAs-based single HBTs, the quaternary In/sub 0.53/Ga/sub 0.34/Al/sub 0.13/As with a wider bandgap is employed as the material for both the base and collector layers. Experimentally, the studied device exhibits a relatively high common-emitter breakdown voltage and low output conductance even at high temperature. Based on the breakdown mechanism of avalanche multiplication, the negative temperature dependence of breakdown voltage is attributed to the positive temperature-dependent impact ionization coefficient. Furthermore, the temperature dependence of current gain is investigated and reported. It is believed that the suppression of hole injection current with decreasing temperature is responsible for the opposite variation of current gains at high current levels.

Temperature-dependent investigation of a high-breakdown voltage and low-leakage current Ga/sub 0.51/In/sub 0.49/P/In/sub 0.15/Ga/sub 0.85/As pseudomorphic HEMT

We reported a newly designed double delta-doped GaInP/InGaAs pseudomorphic HEMT with high temperature-dependent performances. In addition to the novel aspects of the proposed HEMT structure, temperature-dependent behaviors including a high-voltage (40 V) and a low-leakage current (17 nA/mm) are further improved by eliminating mesa-sidewall effect. We obtained nearly current-independent transconductance in the temperature of 300-450 K. The measured current gain cutoff frequency f/sub T/ and maximum oscillation frequency f/sub max/ for a 1-/spl mu/m gate device are 12 and 28.4 GHz, respectively.

Application of selective removal of mesa sidewalls for high-breakdown and high-linearity Ga0.51In0.49P/In0.15Ga0.85As pseudomorphic transistors

High-linearity Ga0.51In0.49P/In0.15Ga0.85As pseudomorphic high electron-mobility transistors have been successfully fabricated and demonstrated in both direct-current and alternating-current performance. Together with a wide-gap Ga0.51In0.49P gate insulator, a gate-to-drain breakdown voltage of 33 V is further improved to over 40 V by selectively removing mesa sidewalls. The transconductance and current density of a 1×100 μm2 device at room temperature (77 K) are 90 (120) mS/mm and 646 (780) mA/mm, respectively. The measured fT and fmax are 12 and 28.4 GHz, respectively. These are consistent with 1 μm gate devices when the parasitic capacitance is reduced by selectively removing mesa sidewalls.

Application of δ-doped wide-gap collector structure for high-breakdown and low-offset voltage transistors

An In0.5Ga0.5P/GaAs double heterojunction bipolar transistor with a δ-doped wide-gap collector structure has been fabricated and studied. Experimental results show that this device exhibits the advantages of a small offset voltage of 50 mV, a small saturation voltage of 1 V, and a large breakdown voltage of 20 V with a current gain of 20. These good characteristics are mainly due to the complete elimination of potential spike at emitter–base and base–collector heterojunctions. Consequently, the studied device shows a good promise for high-speed, high-power, lower-power consumption and large input signal circuit applications.

Investigation of temperature-dependent performances of InP/In0.53Ga0.34Al0.13As heterojunction bipolar transistors

Temperature-dependent dc performances of lattice-matched InP/InGaAlAs heterojunction bipolar transistors (HBTs) using the InGaAlAs quaternary alloy as the base and collector layers are studied and reported. When compared with conventional InP/InGaAs HBTs, the device studied exhibits a higher common-emitter breakdown voltage and a lower output conductance even at high temperature. The variations of offset voltage and ideality factor at different temperatures have been analysed. In addition, with decreasing temperature from 25 °C toward -196 °C, an irregular temperature behaviour of current gain is observed. At high current levels, the temperature-dependent current gain is mainly determined by the reduced reverse hole injection current. As the current level is lowered, the dominance of reverse hole injection current is correspondingly replaced by the recombination current.

Multiple-route and multiple-state current-voltage characteristics of an InP/AlInGaAs switch for multiple-valued logic applications

A novel multiple-state switching device based on an InP/AlInGaAs heterojunction bipolar transistor (HBT) structure has been successfully fabricated and demonstrated. The common-emitter current gain up to 25 is obtained under the forward operation mode. However, the anomalous multiple-negative-differential-resistance (MNDR) phenomena controlled either by electrical or optical input signals are observed under the inverted operation mode. The studied device exhibits a single-route S-shaped NDR behavior in the dark and a distinct significant S-shaped MNDR phenomena by introducing an incident light source at room temperature. Moreover, the anomalous multiple-route and multiple-step current-voltage (I-V) characteristics are also observed at 77 K. The switching behaviors are attributed to the avalanche multiplication, barrier lowering effect and potential redistribution process. Experimental results show that the studied device provides a good potentiality for multiple-valued logic and optoelectronic switching system applications.

High-performance double delta-doped sheets Ga0.51In0.49P/In0.15Ga0.85As/ Ga0.51In0.49P pseudomorphic heterostructure transistors

Novel double delta-doped sheet (D3 S) Ga0.51 In0.49 P/In0.15 Ga0.85 As/Ga0.51 In0.49 P pseudomorphic high-electron-mobility transistors (PHEMTs) have been fabricated successfully and studied. A wide-gap Ga0.51 In0.49 P Schottky layer and a D3 S structure are used to improve device performance. Furthermore, an airbridge-gate structure is employed to achieve good dc and RF performances. For a 1 µm gate length device, a high gate-to-drain breakdown voltage over 35 V, an available output current density up to 615 mA mm-1 , a maximum transconductance of 110 mS mm-1 and a high dc gain ratio of 487 are obtained. On the other hand, the maximum values of unity current gain cut-off frequency fT and maximum oscillation frequency fmax are 19.5 and 40.5 GHz, respectively. The output power of 15.6 dB m (363 mW mm-1 ), power gain of 5.6 dB, power added efficiency (PAE) of 37% and drain efficiency (DE) of 51% are obtained at an input power of 10 dB m and the measured frequency of 2.4 GHz.